CHEYENNE, Wyo. (AP) - A newly published study shows state math and reading tests given to Wyoming's public school students are among the most challenging in the nation.

The study, conducted by Paul E. Peterson and Frederick M. Hess, editors of the quarterly journal Education Next, ranks Wyoming fourth on a list of 40 states.

The study compared how fourth and eighth graders performed on state tests compared with the 2003 National Assessment of Educational Progress test.

State tests are used to rate school performance under the federal No Child Left Behind law. Each state creates its own test and sets the passing score. The result is states with easy tests can appear to be doing well, while those with challenging tests can appear to be doing poorly.

"Some states have risen to the challenge and set demanding proficiency levels for their students, while others have used lower standards to inflate reported performance," the report said. "Not only is the disparity confusing, but, perversely enough, the states with the highest expectations often stand accused of having the most schools said to be in need of improvementeven when their students are doing relatively well."

The top five states in the rankings were South Carolina, Maine, Missouri, Wyoming and Massachusetts.

Ten states were not ranked because they did not have students take the national test.

The Wyoming Department of Education is replacing the Wyoming Comprehensive Assessment System, or WyCas, that has been given to students over the last few years with the Proficiency Assessment of Wyoming Students, or PAWS.

WyCas was taken by students in fourth, eighth and eleventh grades. PAWS will be taken by students in more grades.

On the Net: http://www.educationnext.org.